Sheep and goats infected with 500 or more O. venulosum larvae usually showed diarrhea, and feces containing excessive amts. of mucus, occassionally specked or streaked with blood. There was a slight detrimental effect on the wt. gain of the host. Few or no lesions were noted at necropsy; when present these included petechiae and ulcerative lesions 1 to 2 mm. in diam. in the intestine, and minor adhesions. Partial or complete resistance to reinfection developed as a result of the initial infection. This increased, after the termination of the initial infection, as the period of admn. and number of larvae fed in the initial infection increased.